What are some alternatives?
When comparing DroidEmu and NESBox, you can also consider the following products
RetroArch - RetroArch is a frontend for emulators, game engines and media players.
Nestopia - A portable and cycle-accurate NES emulator written in C++
MESS - Emulates most gaming systems that exist, emphasizing accuracy over speed.
FCEUX - FCEUX is a Nintendo Entertainment System (NES), Famicom, and Famicom Disk System (FDS) emulator.
higan - higan was formerly known as bsnes. The project was renamed after becoming a multi-system emulator.
Mesen - Mesen is a NES/Famicom emulator and NSF player.